1. Field of the Invention
The present invention relates to a control method and a control device as to a gas turbine. More concretely, the present invention relates to a gas turbine control method and a control device thereof for controlling the gas turbine so that the gas turbine is prevented from continuing an operation out of the regular operation line (condition), namely an operation line under an ideal fuel flow rate and air flow rate that are assumed at the design stage of the gas turbine, by adjusting operation control factors so as to restrain the combustion vibrations during the operation of the gas turbine.
2. Background of the Invention
For instance, in a gas turbine driving a generator (an AC generator), the air flow rate and the fuel flow rate toward the combustors of the gas turbine are determined based on the load (the power required by the generator), the ambient temperature, the ambient humidity and so on; and the air flow rate and the fuel flow rate at at-least-one point on the operation line such as a rated operation point are finely adjusted in the trial operation of the gas turbine so that the fine-adjusted air flow rate and fuel flow rate are used as the initial design data (or a protocol condition). However, the period of the trial operation is limited only within a predetermined certain time span; as a matter of course, the trial operations cannot be performed for all the weather conditions that the gas turbine is supposed to encounter. In addition, the actual air flow rate and the fuel flow rate of the gas turbine after being commissioned may deviate from those at the design stage or the trial operation stage due to the secular change such as the deterioration of the compressor performance or the clogging of filters.
On the other hand, the gas turbine is driven by the combustion gas produced through the continuous exothermic oxidation reaction between the fuel and the air supplied into the combustors; thereby, the combustion occasionally accompanies the combustion gas pressure fluctuations of a frequency from 10-Hz to several thousands-Hz, the combustion gas pressure fluctuations including:                the combustion noise caused by the turbulent flow combustion due to the exothermic oxidation reaction, and        the combustion vibration caused by the interaction between the heat dissipation due to the time lag from fuel evaporation to fuel combustion as well as the flame propagation speed change due to combustion gas diffusion and revolution.        
When particular attention is paid to the combustion vibrations, it is recognized that the above-described interaction (between the heat dissipation and the flame propagation speed change) is the vibration source; and, resonance sometimes occurs between the natural frequencies regarding the interaction and the natural frequencies regarding the combustor as an air-column; thus, the combustion vibrations having own frequencies in a peculiar frequency range grow in the combustor. Such combustion vibrations as described are basically unavoidable, whether the strength of the vibration is greater or smaller; and, the strength level depends on the volume of the combustor, the geometry of the combustor, the combustion performance in relation to the combustion gas temperature, and so on.
On the other hand, the demand for further compact and high-powered gas turbines becomes remarkable nowadays. Accordingly, the combustion becomes higher and higher. In order to cope with resulting increased thermal stresses due to the load fluctuations of the gas turbine as well as the rapid temperature increase in the combustor, the heat resisting steel of high strength is used for the combustor and the members therearound; at the same time, in order to reduce the time and manpower regarding delivery, installation, inspection and so on, the less thickness material for its strength is used. As a result, a possibility arises that cracks may be produced on the combustor; the support member may be seriously damaged; the life expectancy as to the configuration members of the gas turbine (or the combustor) may be reduced.
Since such combustion vibrations as described hinder the operation of the gas turbine to a great extent, the countermeasures to restrain or evade the combustion vibrations as far as possible are strongly required in view of plant protection and availability enhancement. Thus, it is essential that the skilled engineers take care of the control system of the gas turbine and confirm the operation stability several times a year so that the combustion stability is maintained and the combustion vibrations do not occur. This practice brings the increase of maintenance cost as well as the decrease of availability.
Against the above-described problems, the patent reference 1 (JP1997-269107), for instance, discloses a combustor combustion vibration control device and a method thereof for restraining the combustion vibrations caused by the pressure fluctuations in the combustor, whereby the device and the method comprising:                a frequency analyzing means that performs frequency analyses as to the pressure fluctuations of the combustion gas,        a central processing unit (means) that computes the conditions (information data) to stabilize the combustion vibrations based on the frequency band in which the result of the pressure fluctuation frequency analyses exists, the pressure fluctuation frequency analyses being performed by the frequency analyzing means;        
a voltage amplification means that amplifies the outputted signals (information data) outputted by the central processing unit (means);                a controlling means that transforms the amplified signals amplified by the voltage amplification means into the order signals to open/close the fuel valves, and transmits the order signals toward the fuel valves.        
The combustion vibration control device and a method disclosed by the patent reference 1 treat with the combustion vibrations of a lower frequency. However, the frequencies of the combustion vibrations occurring in a gas turbine cover a range from a low frequency around 10-Hz to a high frequency of several thousands-Hz; moreover, a plurality of kinds of the combustion vibrations often occurs in a plurality of frequency bands at the same time. Accordingly, if the air fuel ratio as to the gas turbine operation is controlled based on the vibration countermeasure focusing on the low frequency band as per the approach disclosed by the patent reference 1 (JP1997-269107), then there is a possibility that the combustion vibration status in other frequency bands may become worse.
In the patent reference 2 (JP2005-155590), against the background of the above-described problem, the applicants of this specification proposed a gas turbine control device for effectively restraining the combustion vibrations of the gas turbine; in the proposed approach, an order of priority is predetermined, the order relating to which frequency band out of a plurality of frequency bands should be treated so as to restrain the combustion vibrations; in response to the predetermined priorities, the gas turbine operation is adjusted so that the combustion vibrations in a high priority frequency band is controlled; further, the control device is provided with a database that memorizes the information data as to the control adjustments relating to the fuel flow rate and/or the air flow rate supplied into the gas turbine as well as relating to the resulting combustion status changes (caused by the adjustments) in the combustor; moreover, the database is provided with a basic database that stores the information data obtained by the analyses on the basis of the data accumulated in the database; further, on the basis of the data stored in the basic database, at least one of the fuel flow rate and the air flow rate is adjusted (controlled) so that the combustion vibrations are effectively restrained (controlled) even in a case where the combustion vibrations occur in a plurality of frequency bands.
Summing up the main points as for the patent reference 1, the control device and the method thereof treat with the combustion vibrations of a lower frequency; therefore, if the air fuel ratio as to the gas turbine operation is controlled based on the vibration countermeasure focusing on the low frequency band, then there is a possibility that the combustion vibration status in other frequency bands may become worse.
On the other hand, according to the disclosure of the patent reference 2, the combustion vibrations relating to the high priority frequency bands can be effectively restrained; however, there is still a problem; namely, in this approach, the information data as to the control adjustments are stored in the database; similarly, the information data as to the combustion status changes caused by the adjustments are also stored in the database; based on the information data accumulated in the database, the control parameters (variables) are studied (analyzed) as shown in FIG. 12(A); on the basis of the studied data, the control (adjustment) is performed so that the combustion vibrations are restrained; thus, during the adjustments, the efficiency of the gas turbine, for example, is not taken into consideration; as shown in FIG. 12(B), the efficiency is reduced when the adjustments are performed (cf. the right side of FIG. 12(B), namely, the right side with regard to the arrow pointer); in addition, the lateral axis relates to the elapsed time, and the vertical axis relates to the efficiency in FIG. 12(B).
Summing up the main points as for the patent reference 2, the adjustments focus mainly on the vibration countermeasures; thereby, the deviations from the ideal operating point or the ideal operating line as to the initial design stage of the machine are disregarded; similarly, the fatigue life of the machine is also disregarded.
The explanation about FIGS. 12(A) and 12(B) is hereby added. In FIG. 12(A), the lateral axis denotes the load under which the gas turbine is put; the vertical axis denotes the opening of a valve that controls the fuel flow rate or the air flow rate; the points with marks ▪ are the operation points before the adjustments are performed, and the points with marks ▴ are the operation points under stabilized conditions after the adjustments are performed; in a load range from around 90% to around 110% in FIG. 12(A), it can be seen that the valve opening after adjustments becomes greater than that before adjustments; further, in FIG. 12(B) where the lateral axis denotes the elapsed time and the vertical axis denotes the efficiency of the gas turbine, it can be seen that the efficiency falls down in the right side of FIG. 12(B), namely, the right side with regard to the arrow pointer. In other words, since the adjustments are performed so as to restrain the combustion vibrations without consideration regarding ideal operating conditions of the initial design stage, the efficiency drops after the adjustments. The adjustment approach as per the patent reference 2 makes the fuel flow rate valve opening or the airflow rate valve opening deviate from the ideal opening under the ideal initial (delivery or commissioning) condition. Further, in the adjustment approach as per the patent reference 2, the view regarding the fatigue life of the gas turbine is not taken into consideration.
In view of the problems in the disclosed technologies, the present invention aims at providing a gas turbine control method and a device thereof whereby the gas turbine can be prevented from continuing the operation status which is deviated from the ideal operating points regarding the ideal fuel flow rate or the airflow rate, and the gas turbine can maintain the operation status in which the design performance and the gas turbine fatigue life are taken into consideration, the design performance and the gas turbine fatigue life being assumed in the design stage of the gas turbine. In the following paragraphs, the contents of the present invention are disclosed; thereby, the numerals with parentheses (3), (12), (13), and (14) are the component numbers that are later explained in connection with the attached drawings.